1. Field of the Invention
This invention relates to an apparatus and method for continuous application of a hot-melt resin adhesive of the type which becomes flowable at elevated temperatures. The invention has utility generally in the application of hot-melt resin adhesives for metal-to-metal sealing, glass-to-metal sealing, more particularly in the formation of side seams of can bodies and the like as replacement for metallic solders, and in the manufacture of armatures, field windings, and a variety of industrial application involving rapid application of drops of hot-melt resin adhesive to a surface which is to be sealed to another surface.
2. Description of the Prior Art
Apparatus for the application of hot-melt resin adhesives which reach a flowable condition at a temperature of about 250.degree. - 400.degree. F is available and has generally performed satisfactorily. However, such conventional apparatus has proved to be unsatisfactory for use with recently developed hot-melt resin adhesives which require heating to much higher temperatures, e.g. to 600.degree.F or higher, in order to attain a flowable condition suitable for application. It has been found that such resin adhesives undergo oxidation and charring within a relatively short time when used in presently available equipment. Moreover, gaskets, O-rings and similar members of conventional material used in present equipment have shown a tendency to fail under elevated temperature conditions.
Accordingly, it will be evident that there is no presently available apparatus or method for the satisfactory application of hot-melt resin adhesives which become flowable at elevated temperatures, i.e. above about 450.degree.F, without excessive degradation of the resin adhesive.